1. Field of the Invention
The present invention relates to an apparatus and method for fusion bonding works by irradiating them with laser beams.
2. Description of the Related Art
There is a technique for fusion bonding two works, for example, two pieces of glasses by using a laser beam. It is necessary to perform fusion bonding of the glasses when two glass plates are laminated to thereby fabricate a laminated glass, for example.
Referring to FIGS. 10A and 10B, a spacer (not shown) having a minute height is sandwiched between two glass plates 104a and 104b as first and second works. Hence, there is a minute clearance corresponding to the height of the spacer between the two glass plates 104a and 104b. 
A laser machine A100 comprises a work table 103 for fixing the glass plates 104a and 104b thereon, and a machining head 108 for emitting a laser beam (CO2 laser) with which the glass plates 104a and 104b are irradiated. The machining head 108 is movable relatively to the work table 103 in directions of three axes which are orthogonal with one another. The laser machine A100 is configured such that a laser generator 102 generates a laser beam, which is guided to the machining head 108 by mirrors 117 and 118 disposed in appropriate positions on an optical path, and then brought into convergence by an objective lens 119, to thereby irradiate the glass plates 104a and 104b. 
In a fusion bonding process, the two glass plates 104a and 104b are fixed on the work table 103, and the machining head 108 is moved relatively to the work table 103 such that it moves relatively along peripheral portions of the glass plates 104a and 104b while irradiating the peripheral portions represented by oblique lines in FIG. 10A with a laser beam 105. The fusion bonding is completed when the machining head 108 makes a round of the peripheral portions of the glass plates 104a and 104b, resulting in a sealed space between the glass plates 104a and 104b that is shut off from the outside. A gas such as dry air is filled into the space, whereby a highly heat-insulating laminated glass is fabricated.
In the laser fusion bonding method described above, as shown in FIG. 10B, the laser beam 105 with which the glass plates 104a and 104b are irradiated is a convergent beam. For this reason, it is necessary to adjust a spot diameter S of the laser beam 105 on the glass plates 104a and 104b so as to have a size optimal for fusion bonding by moving the machining head 108 in an optical axis direction of the laser beam 105. However, when the machining head 108 is thus moved for adjusting the spot diameter S so as to have the optimal size, deviation relating to its positioning precision occurs, thereby causing a variation of the spot diameter S. In this state, when the spot diameter S is too small due to the variation, a heating range is correspondingly small, leading to unsatisfactory fusion bonding, while when the spot diameter S is too large due to the variation, the temperature of the irradiated spot does not rise to its highest, also leading to unsatisfactory fusion bonding.
The present invention is directed to solving the above problem, and an object of the present invention is to provide an apparatus and method for laser fusion bonding that are capable of reducing unsatisfactory fusion bonding when two works are irradiated with a laser beam to be thereby fusion bonded.
In one aspect of the present invention, there is provided a laser fusion bonding apparatus comprising a laser beam irradiation unit, for fusion bonding portions of at least two works, which are in contact with or close to each other, by irradiating the portions with a laser beam emitted by the laser beam irradiation unit, wherein the laser beam with which the portions are irradiated is a laser beam (hereinafter referred to as a substantially-parallel laser beam) in which rays of light are substantially parallel to one another.
In another aspect of the present invention, there is provided a laser fusion bonding method for fusion bonding portions of at least two works, which are in contact with or close to each other, by irradiating the portions with a laser beam, wherein the laser beam with which the portions are irradiated is a substantially-parallel laser beam.
In the apparatus and the method described above, since the laser beam with which the portions of the works to be fusion bonded (portions to be fusion bonded) are irradiated is the substantially-parallel laser beam, the shapes of spots irradiated with the laser beam in the portions to be fusion bonded are substantially the same even if a distance between the works and a part of the laser beam irradiation unit for emitting the laser beam varies. Thus, unsatisfactory fusion bonding is reduced.
In the apparatus and the method described above, the substantially-parallel laser beam may have a projected shape substantially identical to a predetermined shape so that the spot irradiated with the laser beam in the portions to be fusion bonded has the predetermined shape.
In the apparatus and the method described above, a sectional shape of the laser beam emitted by the laser generator may be converted through the collimation to thereby generate the substantially-parallel laser beam whose projected shape is substantially identical to the predetermined shape. With this configuration, the sectional shape of the substantially-parallel laser beam with which the portions to be fusion bonded are irradiated can be adjusted by the collimation. The collimation is, for example, constituted of collimator lenses, or combination of a concave mirror and a convex mirror.
In the apparatus and the method described above, the sectional shape of the laser beam emitted by the laser generator may be converted through an aperture to generate the substantially-parallel laser beam whose projected shape is substantially identical to the predetermined shape. With this configuration, the sectional shape of the substantially-parallel laser beam with which the portions to be fusion bonded are irradiated can be easily adjusted by varying a shape of an opening of the aperture.
In the apparatus and the method described above, the laser generator may be adapted to generate the substantially-parallel laser beam whose projected shape is substantially identical to the predetermined shape. With this configuration, the structure of the laser irradiation unit can be simplified.
In the apparatus and the method described above, the portions to be fusion bonded may be preheated so as to have a temperature lower than a fusion bonding temperature of the works before the works are fusion bonded by using the substantially-parallel laser beam, and the fusion bonded portions of the works are slowly cooled so as to have a temperature lower than the fusion bonding temperature of the works after the works are fusion bonded by using the substantially-parallel laser beam. With this configuration, since the portions to be fusion bonded are first preheated so as to have the temperature lower than the fusion bonding temperature of the works, the gradient of the temperature in the portions to be fusion bonded and their periphery is gentle. Then, the portions to be fusion bonded are heated so as to have the temperature higher than the fusion bonding temperature. In this case, however, the sharp gradient of the temperature in the works does not occur even if the portions to be fusion bonded has the temperature higher than the fusion bonding temperature, because the periphery of the portions to be fusion bonded is also preheated. Thereafter, the fusion bonded portions are slowly cooled, and thereby the sharp gradient of the temperature in the fusion bonded portions and their periphery caused by rapidly cooling the fusion bonded portions is avoided. As a result, crack due to the sharp gradient of temperature in the works can be reduced. It should be noted that the fusion bonded portions may be slowly cooled while they are heated.
This object, as well as other objects, features and advantages of the invention will become more apparent to those skilled in the art from the following description taken with reference to the accompanying drawings.